Hello there,I'm a N00B in Crystal Space, and I'm currently reading the Crystal Space Manuel 1.4.1I don't know the concept of "portal" in Mazing Tutorial.Is it a concrete portal between two meshes or just a abstract portal between two sectors?

A portal in CS is exactly like the name implies. It is a link to another sector/area. For example, say your application has an exterior world and some buildings with open doors. A portal (which is a polygon) can be placed over the door opening, so that when you enter that building, an image of the outside world is projected onto that polygon instead of rendering out the entire outside world. Portals, like in the example, can be used for efficiency or for creativity (such as teleporting to different locations when you go through one), but are ultimately unnecessary, especially for small, resource insignificant applications. The maze tutorial has them merely as a demonstration of their use. Play around with them and you'll get the hang of it.